Heat transfer tubes with grooved inner surfaces are used primarily as evaporator tubes or condenser tubes in heat exchangers for air conditioning and refrigeration. It is known to provide heat transfer tubes with grooves and alternating “fins” on their inner surfaces. The grooves and the fins cooperate to enhance turbulence of fluid heat transfer mediums, such as refrigerants, delivered within the tube. This turbulence enhances heat transfer performance. The grooves and fins also provide extra surface area and capillary effects for additional heat exchange. This basic premise is taught in U.S. Pat. No. 3,847,212 to Withers, Jr. et al.
It is further known in the art to provide internally enhanced heat exchange tubes made by differing methods; namely—seamless tubes and welded tubes. A seamless tube may include internal fins and grooves produced by passing a circular grooved member through the interior of the seamless tube to create fins on the inner surface of the tube. However, the shape and height of the resulting fins are limited by the contour of the circular member and method of formation. Accordingly, the heat transfer potential of such tubes is also limited.
A welded tube, however, is made by forming a flat workpiece into a circular shape and then welding the edges to form a tube. Since the workpiece may be worked before formation when flat, the potential for varying fin height, shape and various other parameters is increased. Accordingly, the heat transfer potential of such tubes is also increased.
This method of tube formation is disclosed in U.S. Pat. No. 5,704,424 to Kohn, et al. Kohn, et al. discloses a welded heat transfer tube having a grooved inner surface. In the described and claimed production method, a flat metallic board material is rounded in the lateral direction until the side edges are brought into contact with each other. At that point, the two edges of the board material are electrically seam welded together to form the completed tube. As stated therein, an advantage of this method is that any internal fins or grooves can be embossed onto one side of the tube while the metallic board is still flat, thereby permitting increased freedom of design attributes.
Such design freedom is a key consideration in heat transfer tube design. It is a common goal to increase heat exchange performance by changing the pattern, shapes and sizes of grooves and fins of a tube. To that end, tube manufacturers have gone to great expense to experiment with alternative designs. For example, U.S. Pat. No. 5,791,405 to Takima et al. discloses a tube having grooved inner surfaces that have fins formed consecutively in a circumferential direction on the inner surface of the tube. A plurality of configurations are shown in the various drawing figures. U.S. Pat. Nos. 5,332,034 and 5,458,191 to Chiang et al. and U.S. Patent No. 5,975,196 to Gaffaney et al. all disclose a variation of this design referred to in this application as a cross-cut design. Fins are formed on the inner tube surface with a first embossing roller. A second embossing roller then makes cuts or notches cross-wise over and through the fins. This process is costly as at least two embossing rollers are required to form the cross-cut design. Moreover, the fins disclosed in all of the designs of these patents are separated by empty troughs or grooves. None of the designs capitalize on this empty area to enhance the heat transfer characteristics of the tubes.
While these inner surface tube designs aim to improve the heat transfer performance of the tube, there remains a need in the industry to continue to improve upon tube designs by modifying existing and creating new designs that enhance heat transfer performance. Additionally, a need also exists to create designs and patterns that can be transferred onto the tubes more quickly and cost-effectively. As described hereinbelow, the applicant has developed new geometries for heat transfer tubes and, as a result, significantly improved heat transfer performance.